1. Field of the Invention
The present invention relates to an LSI device etching method and apparatus for treating LSI devices by making use of plasma.
2. Description of Relevant Art
With the rapid advancement in finer sizes and higher integration, LSI devices with a gate length of 0.13 μm have been shifted to mass production, and LSI devices with sizes of 90 or 65 nm are being developed. For high speed operation of LSI devices, it is necessary to achieve an improvement in the operation speed of the transistors and to overcome the propagation delay (so-called RC delay) of multilayer metal interconnection. In recent years, the propagation delay of interconnection is becoming more and more influential.
As a solution means, Cu interconnection having a low resistivity ρ and a low-k film having a low relative permittivity k of the capacitor part are being developed. Since CuClx, a chloride of Cu, is low in steam pressure, plating technique or the like have been generally used for formation of the Cu interconnection. In recent years, the technique, such as Dual Damascene method, by which an interconnection and a via-part are simultaneously formed in order to provide a multilayer interconnection structure, has been developed. As the low-k film, such films as HSQ (Hydrogen Silsequioxane), MSQ (Methyl Silsequioxane), polysiloxane and others are being developed to achieve relative permittivity k<3.0. In addition, a porous insulator film having pores inside is also now being used.
In the multilayer interconnection structure having a combination of Cu interconnection and a low-k film of the damascene structure, it is necessary to provide a diffusion prevention film to suppress the diffusion of Cu. The diffusion prevention film can be SiN, SiON, SiC, SiOC, SiCN, or the like. Cu easily diffuses into Si (Poly-Si, intrinsic Si, amorphous Si, or SiC in parts) composing transistors or into a capacitor SiO2 (low-k film). When Cu diffuses into Si, it affects the band gap of Si and causes a fluctuation in electric properties. Thus, when Cu diffuses into the low-k film, Cu becomes the seed of polarization, whereby the relative permittivity increases. This is why the presence of the diffusion prevention film is important.
When forming a low-k film onto Cu interconnection, in the multilayer interconnection structure, there are various combinations between the type and structure of the diffusion prevention film and the low-k film. As one example, the multilayer interconnection structure, in which a first low-k film, a Cu interconnection, a diffusion prevention film, and a second low-k film are formed in this order, can be cited. Here, first and second low-k films are often made of the same material. In general, the diffusion prevention film has a higher dielectric constant than the low-k film, therefore the diffusion prevention film is preferably thinner.
When etching is conducted to form a contact hole for providing an interconnection in this diffusion prevention film, it is necessary to have a large etching selectivity between the diffusion prevention film and the low-k film. That is, it is necessary one of the diffusion prevention film and the low-k film is selectively etched. In this occasion, the diffusion prevention film also functions as an etching stopper film.
These descriptions regard to the case of the etching of the film having the damascene structure including Cu interconnection and a low-k film. In the case of the etching of the Si-containing mask material, it is also necessary to increase the etching selectivity between the mask material and the underlying film (the resist or the low-k film).
In Japanese Unexamined Patent Publication 2002-110644 (equivalent to U.S. Pat. No. 6,617,244), a method for performing the etching of the multilayer interconnection structure, which includes an underlying interconnection layer, a SiC layer provided thereon, an interlayer insulator film layer, a via-hole, and an interconnection trench, is disclosed. In this method, a nitrogen-containing gas is added to a halogen compound-containing etching gas in order to perform the dry-etching of the SiC layer, during etching a multilayer interconnection structure. In this method, NF3, SF6, CF4, CHF3, CH2F2, oxygen, nitrogen, ammonium, and nitrous oxide are used as examples of the gas to be mixed to the etching gas.
In Japanese Unexamined Patent Publication H07-169747, for example, a method for etching SiO2 film is disclosed. In this method, a mixture of a chlorofluorocarbon-based gas and a sulfur-based gas not containing fluorine, such as SO, SO2, SO3 and others, are used.
In case of Japanese Unexamined Patent Publication 2002-110644, the gases, such as NF3 or CF4, are used for etching SiC. In this case, although SiC can be etched at a high speed when NF3 is used solely, the etching selectivity of SiC to the interlayer insulator film typified by SiOC, which should not be etched, is as low as 2 or so. This selectivity can be obtained in the case of CF4, and can be improved by increasing the amount Of O2 gas to be added.
In this case, however, the etching speed of SiC, which is the film to be etched, decreases monotonously. Even if the etching rate is sacrificed and set to a level not more than 100 nm/min, the etching selectivity cannot be higher than 4.
In the case of Japanese Unexamined Patent Publication H07-169747, the film to be processed is SiO2, and there are no considerations of etching of SiC and achieving a high etching selectivity of SiC to SiOC.
Therefore, an etching process and apparatus which, during etching a multilayer interconnection structure (damascene structure), can increase the etching selectivity (preferably 8 or larger) of the diffusion prevention film (etching stop film) to the low-k film and also increase the etching speed (200 nm/min or higher) of the diffusion prevention film, have been required.
Additionally, an etching process and apparatus which, during etching a mask material, can increase the etching selectivity of the mask material to the underlying film (the resist or the low-k film) or increase the etching speed of the mask material, have been required.